This invention is in the field of polymer compositions, and processes; more particularly, the invention relates to ultrahigh molecular weight polymer compositions, particularly ultrahigh molecular weight polyethylene compositions, and methods of melt processing such as continuously forcing the composition through an aperture such as by extrusion.
Ultrahigh molecular weight polyethylene is described as high density polyethylene with an extremely high molecular weight in the range of two to six million, by Hug D. P., "UHMW polyethylene", Modern Plastics Encyclopedia, 1979-80, Vol. 56, No. 10A, pp. 74-76 published by McGraw-Hill and hereby incorporated by reference. It is noted in this article that ultrahigh molecular weight polyethylene cannot be processed by conventional plastic processing techniques. The long chain molecules do not melt or flow in a normal thermoplastic manner.
The Hug article notes that a method has been developed to injection mold ultrahigh molecular weight polyethylene in a specially designed machine which is a modification of a standard scew-injection molding machine. Other new processes have been disclosed by which special equipment can be used to process ultrahigh polyethylene.
As indicated in the Hug article there are a variety of known ultrahigh molecular weight compositions. Filler and polymer modifiers can be added to enhance certain properties.
U.S. Pat. No. 4,420,580 discloses that the detrimental effect of inorganic metal fillers on the impact strength of polyolefin resins is reduced by the addition of a copolymer of ethylene and an alpha,beta-ethylenically unsaturated carboxylic acid, such as ethylene acrylic acid, to a melt blend of polyolefin resin containing the inorganic filler. The ethylene copolymer is added to compatibilize or couple the filler into the polyolefin resin. This disclosure is not directed to ultrahigh molecular weight polymers nor is there a recognition of the use of the inorganic metal filler and acid copolymer to lubricate the polyolefin.